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ZINC PLATING AND OLIVE BLACK PASSIVATION (CHROMATING)
Hello everyone,
Can anybody clear my query as given below.
After Zinc plating & Olive black passivation on steel fasteners & fine blanked components (structural steel which are copper brazed with En8 material):
1. We face the problem on colour inconsistency - olive black not proper.
2. Also colour retentivity (i.e. after a few days olive black turns complete black).
3. Blister formation.
4. What should be the surface finish in the component.
5. What is the optimum plating thickness.
6. We require brake fluid compatibility( DOT3 & DOT 4 ).
7. What are the chemicals, their percentage etc. required to overcome the above problems.
8. How far the intricate components get affected compared to plane surfaces.
9. What is the expected life of components in NSS test.
- Coimbatore, Tamil Nadu, India
Dear cousin Senthil,
I doubt that the readers will offer much response to your inquiry. I say that not as criticism of the readers or of you, but to explain why inquiries like yours often go unanswered, and to explain how I think you might be able to elicit better response to your needs if you wish. This site is a place of camaraderie where peers exchange information and work together towards solving finishing problems. You've not yet helped anyone else with their inquiries, whereas your first inquiry has 9 different broad-ranging requests. People may feel little sense of obligation to spend half an hour helping people go into competition with them, especially when that person hasn't taken the time to see if there is a way to reciprocate. But anyway . . .
What proprietary olive black chromate or home brew formula do you use that turns black? What kind of zinc plating do you do--acid, alkali, or cyanide? What surface finish do you get now now? What thickness do you plate now? Do you have brake fluid compatibility now? What thickness ratio do you get between the HCD and LCD areas now? What NSS life do you get now? Thanks!
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 Ted Mooney, P.E. finishing.com Brick, New Jersey |
The plating system has two main parts to it: the main zinc plating, and the passivation. The thickness of the plating depends on your application. The auto parts we work with get around 8 microns of plating. The passivate is not specified by thickness.
Some of these technical issues should be addressed with your plating supplier. They should understand their processes well and should be able to educate you a bit on issues like this. You can also refer to the Metal Finishing Guidebook from Metal Finishing Magazine. This guidebook gives generic technical explanations of plating and of conversion coatings (passivation).
Sometimes is is very hard to produce an exact color consistently. The color is dependent on the passivation, not necessarily the plating part. As you make part after part, the chemicals in the bath deplete, and the concentrations change over time. It can be difficult to maintain the passivation chemical bath the same all day every day. You may want to relax your color requirements to make things much easier for your plater. The plater may not have the capability to meet tight color requirements.
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Tim Neveau Rochester Hills, Michigan |